A conventionally widely employed method for radiating heat generated from a heat-generating electronic component of electronic equipment uses an aluminum heat radiation substrate whose one side serves as a heat-receiving surface to be thermally brought in contact with the heat-generating electronic component and which has heat radiation fins provided integrally with the other side thereof. The heat-generating electronic component is mounted on the heat-receiving surface of the heat radiation substrate. Wind is blown against the heat radiation fins by means of a cooling fan, thereby releasing heat generated from the heat-generating electronic component into the air via the heat radiation substrate and the heat radiation fins.
However, because of a tendency of an increased amount of heat generated from heat-generating electronic components used in recent electronic equipment associated with implementation of reduced sizes and higher performance, the conventional method has been encountering difficulty in providing sufficient heat radiation performance. Also, notebook-size personal computers, two-dimensional display units, projectors, and the like have been increasing in noise of cooling fans and thus have been encountering difficulty in fulfilling required quietness.
In order to solve the above problems, the applicants of the present invention proposed a liquid-cooled heat radiator which uses a water-containing cooling liquid; for example, antifreeze (refer to Patent Document 1). The liquid-cooled heat radiator described in Patent Document 1 includes a heat radiation base composed of two aluminum plates brazed together in layers and having a cooling-liquid channel; an expansion tank provided on the heat radiation base; and a pump for circulating antifreeze through the cooling-liquid channel. The heat radiation base has, on its one side, a heat-receiving region with which a heat-generating body to be cooled by the cooling liquid flowing through the cooling-liquid channel is thermally brought in contact. The cooling-liquid channel is formed by outwardly expanding at least one of the two aluminum plates. The expansion tank has a tank body having an expanded portion, which expands upward and opens downward, and a bottom plate joined to the lower end of the tank body to thereby close a bottom opening of the expanded portion, and joined to the upper surface of the heat radiation base. The heat radiation base and the bottom plate have respective communication holes formed therein for establishing communication between the cooling-liquid channel and the interior of the tank body.
Meanwhile, the antifreeze is noncorrosive to aluminum, but may generate hydrogen through reaction between water and aluminum. So long as the amount of generated hydrogen is small, generated hydrogen is collected within the tank body of the expansion tank, thereby preventing increase in pressure in the cooling-liquid channel. However, because of the limitation of the effect of preventing increase in pressure in the cooling-liquid channel by means of the expansion tank, an increase in the amount of generated hydrogen may cause the pressure in the cooling-water channel to exceed an allowable pressure, potentially causing a malfunction of the pump.
Patent Document 1: Japanese Patent Application Laid-Open (kokai) No. 2005-167224